1. Field of the Invention
The present invention relates to a method of making a top spin valve sensor with an in-situ formed seed layer structure for improving sensor performance and, more particularly, to a method of making such a seed layer structure by ion beam depositing first and second seed layers in a sputtering chamber without breaking a vacuum in the chamber between the depositions.
2. Description of the Related Art
The heart of a computer is an assembly that is referred to as a magnetic disk drive. The magnetic disk drive includes a rotating magnetic disk, a slider that has read and write heads, a suspension arm above the rotating disk and an actuator that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent an air bearing surface (ABS) of the slider causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk. When the slider rides on the air bearing the write and read heads are employed for writing magnetic impressions to and reading magnetic impressions from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
The write head includes a coil layer embedded in first, second and third insulation layers (insulation stack), the insulation stack being sandwiched between first and second pole piece layers. A gap is formed between the first and second pole piece layers by a nonmagnetic gap layer at an air bearing surface (ABS) of the write head. The pole piece layers are connected at a back gap. Current conducted to the coil layer induces a magnetic field into the pole pieces that fringes across the gap between the pole pieces at the ABS. The fringe field writes information in the form of magnetic impressions in circular, tracks on the rotating disk.
An exemplary high performance read head employs a spin valve sensor for sensing magnetic signal fields from the rotating magnetic disk. The sensor includes a nonmagnetic electrically conductive first spacer layer sandwiched between a ferromagnetic pinned layer and a ferromagnetic free layer. An antiferromagnetic pinning layer interfaces the pinned layer for pinning the magnetic moment of the pinned layer 90.degree. to an air bearing surface (ABS) which is an exposed surface of the sensor that faces the rotating disk. First and second leads are connected to the spin valve sensor for conducting a sense current therethrough. A magnetic moment of the free layer is free to rotate upwardly and downwardly with respect to the ABS from a quiescent or zero bias point position in response to positive and negative magnetic signal fields from the rotating magnetic disk. The quiescent position of the magnetic moment of the free layer, which is preferably parallel to the ABS, is when the sense current is conducted through the sensor without magnetic field signals from the rotating magnetic disk. If the quiescent position of the magnetic moment is not parallel to the ABS the positive and negative responses of the free layer will not be equal which results in read signal asymmetry which is discussed in more detail hereinbelow.
The thickness of the spacer layer is chosen so that shunting of the sense current and a magnetic coupling between the free and pinned layers are minimized. This thickness is typically less than the mean free path of electrons conducted through the sensor. With this arrangement, a portion of the conduction electrons is scattered by the interfaces of the spacer layer with the pinned and free layers. When the magnetic moments of the pinned and free layers are parallel with respect to one another scattering is minimal and when their magnetic moments are antiparallel scattering is maximized. An increase in scattering of conduction electrons increases the resistance of the spin valve sensor and a decrease in scattering of the conduction electrons decreases the resistance of the spin valve sensor. Changes in resistance of the spin valve sensor is a function of cos .theta., where .theta. is the angle between the magnetic moments of the pinned and free layers. The sensitivity of the sensor is quantified as magnetoresistance or magnetoresistive coefficient dr/R where dr is the change in resistance of the spin valve sensor from minimum resistance (magnetic moments of free and pinned layers parallel) to maximum resistance (magnetic moments of the free and pinned layers antiparallel) and R is the resistance of the spin valve sensor at minimum resistance. A spin valve sensor is sometimes referred to as a giant magnetoresistive (GMR) sensor.
One of the magnetic fields affecting the aforementioned read signal symmetry is a ferromagnetic coupling field H.sub.FC between the pinned and free layers. Because of the thinness of the spacer layer between the pinned and free layers the ferromagnetic coupling field exerted on the free layer is typically in the same direction as the magnetic moments of the pinned layer. Since the ferromagnetic coupling field on the free layer is perpendicular to the ABS this field urges the magnetic moment of the free layer from a desired direction parallel to the ABS, which denotes read signal symmetry when the sensor is in a quiescent condition, to a direction which is between parallel and perpendicular positions with respect to the ABS. Accordingly, it is desirable to minimize the ferromagnetic coupling field in order to promote read signal symmetry.
Another factor affecting the performance of a spin valve sensor is the coercivity H.sub.C of the free layer. This is the amount of field that is required to saturate the magnetic moment of the free layer in the easy axis direction. It is desirable that the coercivity H.sub.C of the free layer be low so that the magnetic moment of the free layer readily responds to signal fields from the rotating magnetic disk. When the coercivity H.sub.C is high the free layer is referred to as being stiff in its operation since the magnetic moment rotates only ga slight distance from its parallel position in response to signal fields from the rotating magnetic disk. A greater rotation of the magnetic moment of the free layer in response to signal fields results in greater positive and negative resistances of the spin valve sensor to the sense current I.sub.S which equates to greater playback signals.
Spin valve sensors are classified as either a top spin valve sensor or a bottom spin valve sensor. In a top spin valve sensor the free layer is located closer to the first shield layer than to the second shield layer and in a bottom spin valve sensor the free layer is located closer to the second shield layer than to the first shield layer. Spin valve sensors are further classified as having a single pinned layer or an antiparallel (AP) pinned layer structure. A single pinned layer may comprise one or more ferromagnetic films interfacing one another whereas in an AP pinned layer structure an antiparallel coupling layer, such as ruthenium (Ru), is located between first and second ferromagnetic layers. The AP pinned layer structure exerts a net demagnetizing field which is less than a demagnetizing field from the single pinned layer structure since the first and second ferromagnetic layers of the AP pinned layer structure have partial flux closure.
Efforts continue to improve the magnetoresistive coefficient dr/R, reduce the ferromagnetic coupling field HFC between the pinned and free layers, and reduce the coercivity H.sub.C of the free layer for improving the performance of the spin valve sensor. These types of efforts have improved the magnetic storage capability of computers from kilobytes to megabytes to gigabytes.